The invention is related to storage systems in general, and more specifically to data replication in storage systems.
Some organizations copy data from primary site (production site) to one or more secondary sites in preparation for data collapse or disaster. When the primary site fails due to some trouble such as disaster and the primary storage becomes unavailable, computer systems start their jobs using data in secondary storage.
U.S. Pat. Nos. 5,544,347 and 6,408,370 (incorporated herein by reference for all purposes) disclose remote mirroring methods in which the primary storage systems transfer data to the secondary storage systems. These references describe a system in which both the primary and secondary storage systems each has the same remote mirroring functions as in the other. The primary storage system transfers data to be mirrored by attaching additional information that is needed for remote mirroring. The secondary storage system (e.g., SECONDARY DATA DESTAGING UNIT in U.S. Pat. No. 6,408,370) attempts to preserve the write order of the remote copy data by interpreting the additional information that is attached to the remote copy data.
European Patent publication EP 0672985A1 discloses another remote mirroring method. In the system in EP 0672985A1, host computers take charge of mirroring data between the primary and secondary sites. This method, however, burdens host computers with the workload required to effect the data mirroring functionality.